The present invention is generally directed to an antenna for communicating electromagnetic signals, and relates more particularly to a planar array antenna having patch radiators disposed within a compact volume for increasing RF bandwidth and beamwidth.
Antenna designers are often forced to design antennas in a backward fashion. For example, because of the increasing public concern over aesthetics and the xe2x80x9cenvironmentxe2x80x9d, antenna designers are typically required to build an antenna in accordance with a radome that has been approved by the general public, land owners, government organizations, or neighborhood associations that will reside in close proximity to the antenna. Radomes are typically enclosures that protect antennas from environmental conditions such as rain, sleet, snow, dirt, wind, etc. Requiring antenna designers to build an antenna to fit within a radome as opposed to designing or sizing a radome after an antenna is constructed creates many problems for antenna designers. Stated differently, the antenna designer must build an antenna with enhanced functionality within spatial limits that define an antenna volume within a radome. Such a requirement is counterproductive to antenna design since antenna designers recognize that the size of antennas are typically a function of their operating frequency. Therefore, antenna designers need to develop high performance antennas that must fit within volumes that cut against the ability to size antenna structures relative to their operating frequency.
Conventional antenna systems confined within predefined volumes, such as radomes, usually cannot provide for large beamwidths in addition to large bandwidths. In other words, the conventional art typically requires costly and bulky hardware in order to provide for a wide beamwidths and bandwidths, where beamwidth is measured from the half-power points (xe2x88x923 dB to xe2x88x923 dB) of a respective RF beam. Such bulky and costly hardware usually cannot fit within very small, predefined volumes.
Another drawback of the conventional art relates to the manufacturing of an antenna system and the potential for passive intermodulation (PIM) that can result because of the material used in conventional manufacturing techniques. More specifically, with conventional antenna systems, dissimilar materials, ferrous materials, metal-to-metal contacts, and deformed or soldered junctions are used in order to assemble a respective antenna system. Such manufacturing techniques can make an antenna system more susceptible to PIM and therefore, performance of a conventional antenna system can be substantially reduced.
Accordingly, there is a need in the art for a substantially compact antenna system that can fit within a predefined volume and that can generate relatively wide RF radiation patterns and increased RF bandwidth. Further, there is another need in the art for a compact antenna system that can be manufactured with ease and that can utilize manufacturing techniques which substantially reduce passive intermodulation. There is an additional need in the art for a substantially compact antenna system that can handle the power characteristics of conventional antenna systems without degrading the performance of the antenna system.
The present invention solves the aforementioned problems with an antenna system that can generate large and wide RF radiation fields in addition to providing increased bandwidth. This enhanced functionality can be achieved with a compact antenna system, where the antenna system without a radome can typically have a height of less than one seventh ({fraction (1/7)}) of a wavelength and a width that is less than or equal to six-tenths (0.6) of a wavelength. With an antenna radome, the antenna system can have a height that is less than or equal to one-fifth (⅕) of a wavelength. The antenna system can comprise one or more patch radiators separated from each other by an air dielectric and by relatively small spacer elements. The patch radiators can have predefined shapes for increasing beamwidths.
In one exemplary embodiment, the patch radiators can have a substantially rectangular shape. One or more lower patch radiators can be mounted to a printed circuit board that can comprise an RF feed network and a ground plane which defines a plurality of symmetrically, shaped slots. In one exemplary embodiment, the slots can comprise a xe2x80x9cdog-bonexe2x80x9d or xe2x80x9cdumbellxe2x80x9d shape that has an electrical path length that is less than or equal to a half wavelength.
The slots within the ground plane of the printed circuit board can be excited by stubs that are part of the feed network of the printed circuit board. The slots, in turn, can establish a transverse magnetic mode of RF radiation in a cavity which is disposed adjacent to the ground plane of the printed circuit board and a ground plane of the antenna system.
The cavity can be concentrically aligned with geometric centers of the patch radiators. The feed network of the printed circuit board can be aligned with portions of the cavity such that the portions of the cavity function as a heat sink for absorbing or receiving thermal energy produced by the feed network. Because of this efficient heat transfer function, the printed circuit board can comprise a relatively thin dielectric material that is typically inexpensive.
The cavity disposed between the printed circuit board and the ground plane of the antenna system can function electrically as a closed boundary when mechanically, the cavity has open comers. The open comer design facilitates ease in manufacturing the cavity. The open comers of the cavity can also have dimensions that permit resonance while substantially reducing Passive Intermodulation (PIM).
PIM can be further reduced by planar fasteners used to attach respective flanges and a planar center of a respective cavity to the ground plane of the printed circuit board and the ground plane of the antenna system. The planar fasteners can comprise a dielectric adhesive. In addition to the dielectric adhesive, the present invention can also employ other types of fasteners that reduce the use of dissimilar materials, ferrous materials, metal to metal contacts, deformed or soldered junctions and other similar materials in order to reduce PIM.
For example, the patch radiators can be spaced apart by plastic fasteners that permanently xe2x80x9csnapxe2x80x9d into place. Such fasteners not only reduce PIM, but also such fasteners substantially reduce labor and material costs associated with the manufacturing of the antenna system.
In one exemplary embodiment, a radome is placed over the patch radiators. Radomes are typically designed to be electrically transparent to the radiators of a antenna system. However, for the present invention, when a radome is placed over the patch radiators, an unexpected result occurs: the performance of the patch radiators is increased. More specifically, return loss is improved and peak gain is higher relative to an antenna without a radome. Further, upper side lobe suppression is improved compared to an antenna without a radome.
While providing a product that can be manufactured efficiently, the present invention also provides an efficient RF antenna system. The RF energy produced by the cavity, slots, and stubs can then be coupled to one or more patch radiators. The patch radiators can then resonate and propagate RF energy with relatively wide beamwidths and increased bandwidth.